It works both on Android and iOS. Although it's not yet published on Apple Store. You can find the Android app here at the Google Play Store.

The backend server itself it's pretty simple, in the Docs folder you can find all the json schemas for the routes you have to serve.

Ther's a simple test server written in node.js published with the application code, you can find it in the appdressbookapisample folder. I've implemented a C# server for my company. Building the API server is really a simple job. Contacts can be secured by username and password validation. Contacts can of course be synced according to the logged in user. You can even chose to deploy your contacts without authentication.

When the application is executed for the first time, the API server must be filled. Then that server is beeing asked for settings. If authentication is required user has to authenticate, if not contacts can be synced instantly.

Contacts list is cheked against the server each 10 minutes, using the hash of the list, this is to prevent bandwith consumption.